The surfaces of tubes, cables or cylindrical bars frequently require machining prior to further processing thereof. Thus for example in the case of cables it is necessary to remove an insulating layer while when welding plastic tubes the surface of the tubes has to be shaved off prior to the welding operation. In that situation a layer of the order of magnitude of between about 0.5 mm and 0.3 mm (and even deeper, in dependence on large tubes) is removed in the regions which are to be welded together. That procedure results in the removal of dirt inclusions from the manufacturing process and ageing-induced changes in the material, which can occur for example due to UV-damage or weathering at the surface and which would otherwise result in unsatisfactory welding results.
In order to be able to precisely remove a surface layer which is as thin as possible from the article to be machined, the cutting depth of the blade must be precisely adjusted. Such adjustment of the blade, which is necessary upon a change in the cutting depth and also upon a change in blade, requires skill and great experience on the part of the operator. If the blade is wrongly oriented, frequently an only inadequate machining quality is achieved. Then, either too much material is removed from the articles to be machined, whereby for example in the case of tubes the remaining cross-section is possibly unacceptably reduced, or the surface layers which are damaged due to dirt inclusions or ageing are not completely removed. If the blade is oriented in an inclined manner, it is then possible that unwanted grooves or channels are left behind on the article to be pared, and they can adversely affect the welding.
Tubular rolled coil material, due to the manner of manufacture involved, has a certain degree of ovality which also occurs in the case of tubular bar material due to prolonged storage times. That tube ovality is unwanted in the paring operation as, with a fixedly set spacing between the support unit and the paring unit, with the blade arranged thereon, the removal of material becomes irregular and untidy so that it is not possible to achieve satisfactory machining results. In extreme cases regions of the tube can remain unmachined while other regions of the tube are shaved off to an unacceptably great depth.
In order to remove the surface layer from tubes or the like, German utility model 93 05 220 U discloses a paring apparatus of the kind set forth in the opening part of this specification, in which the paring blade is fixedly connected to the paring head. In that paring apparatus the cutting depth of the paring blade must be accurately adjusted in order to be able to shave off exactly a surface layer which is as thin as possible, from the article to be machined. That adjustment procedure is necessary upon each change in the cutting depth and also when changing the blade, in order to ensure that incorrect orientation of the paring blade does not give rise to an only inadequate machining quality. As a consequence of the rigid connection of the paring blade to the paring head and thus to the guide element in the form of a roller, the paring blade, when dealing with deformed articles, in particular when there are raised portions and depressions on the article to be pared, can be lifted out of the material so that unpared locations remain on the article to be pared.
European patent application No 01 113 726 further discloses a paring apparatus which has been improved over the paring apparatus described in German utility model No 93 05 220, insofar as the blade assembly with the paring blade is adapted to be resilient and tiltable. In addition that arrangement has a spring element for compensating for ovality. Therefore a satisfactory paring result can be achieved with that known paring apparatus, when dealing with slightly deformed articles.
In the case of severely deformed tubes, however, unpared locations still remain behind even when using that paring apparatus. That is to be attributed to the fact that the necessary sliding shoes lift the sprung blade out of the material to be pared, at locations having raised portions or recesses.
The object of the present invention is to provide a paring apparatus of the kind set forth in the opening part of this specification, which, even in the case of severely deformed tubular articles, permits the outer skin of that article to be satisfactorily pared off, in particular without unpared locations.